The purpose of this proposal is to understand how maternal factors are unequally localized in the embryos and thereby defining the polarities of the embryo and the fates of the blastomeres in C. elegans. During early C. elegans embryogenesis, PIE-1 protein is localized exclusively to germline blastomeres. In this proposal we will identify factors that regulate unequal localization of PIE-1 in the C. elegans embryo. These factors will help us to build molecular models on the mechanism of cell polarity and germ cell specification. In a preliminary study, we have already identified two very intriguing proteins, ALP-1 and UBC-9, which suggested that translational regulation and post-translational modification may be involved in this process. More importantly, PI3-1, ALP-1 and UBC-9 all have homologues in other organisms, suggesting that there may be conserved mechanism in generating asymmetry in cells that leads to asymmetric division. To understand the mechanism of asymmetric division in which two daughter cells with different developmental potentials are produced is of basic fundamental importance in developmental biology. This research is also relevant to human development and fertility as well as to mechanisms of stem-cell renewal and oncogenesis.